Protective device for vent stack



Jan. 25, 1966 R. D. REED ETAL PROTECTIVE DEVICE FOR VENT STACK Filed Jan. 6, 1964 M Y ma m w 0 W m am MM 5 .BN mm F m M Q 4 m 6 F United States Patent "ice 04 PROTECTIVE DEVICE FOR VENT STACK Robert 1). Reed and John Smith Zink, Tulsa, Okla, assigners to John Zink Company, Tulsa, Okla, a corporation of Delaware Filed Jan. 6, 1964, Ser. No. 335,985 4 Claims. (Cl. 158--99) This application is a continuation-in-part of our copending application Serial No. 52,562, filed August 29, 1960, now abandoned.

The present invention pertains to a device mounted on the upper end portion of a vertically disposed conduit or stack having an open upper end through which gaseous materials are vented to the atmosphere or through which gaseous materials escape for burning and the device serves to prevent such materials from being drawn downwardly onto the leeward part of the conduit and into a low pressure zone developed at the downwind side of the stack.

It is customary for a flare stack burner or a similar vertically disposed conduit for venting waste gaseous materials to the atmosphere to have their upper ends disposed at significant elevations above the surrounding terrain. .The pressure e'xteriorly of such a stack at the upwind side thereof is greater than atmospheric pressure and the pressure at the leeward side of the conduit is less than atmospheric pressure when there is movement of the air at an appreciable velocity transversely of the conduit such as takes place when there are wind currents. The increased pressure at the windward side of the stack is the result of the impact of the air moving thereagainst and the low pressure at the leeward side of the stack is developed by the acceleration of the 'air moving about or around the stack structure to provide a void at the downwind side thereof. When such a conduit is employed as a flare stack burner the low pressure'condition developed at the leeward side causes the burning gases to be drawn into the low pressure zone and over the exterior or the stack. When such a conduit serves as a smoke stack or to vent gases to the atmosphere such gases are drawn into the low pressure zone into the presencewf the conduit structure. There'is accordingly a corrosive attack of the structure of the conduit and when it is employed for burning gases heat is also drawn into the low pressure zones to further promote deterioration of the stack structure. It is an object of the present inventionto provide means on such a vertically disposed conduit for avoiding the development of a low pressure condition at the leeward side. of the stack in the vicinity of the upper end thereof and to thereby prevent corrosive gases or products of combustion or the like being drawn into the presence of the s'ta'ck structure at the leeward side of the upper end thereof.

A morespecific object of the invention is to provide a device in surrounding relationship with the upper end of a conduit which is soco'nstructed and supported on the stack structure as to provide 'an increase in the pressure at the leeward side and exteriorly of thest'ack adjacent the upper end thereof when there is wind actioncausing air to move transversely of the stack structure.

A further object of the invention is to provide a generally cup-shaped device in "surrounding relationship with the upper end of a vertical disposed conduit which is provided withopenings so disposed and shaped and with the flow coefficient thereof serving to prevent the escape of the air from the cup-shaped member at the same rate at which it enters and to thereby build up the pressure at the downwind side of the stack and to provide for an upward flow of air at the leeward. side of the conduit to prevent the vented gases or products of combustion from 3,231,004 Patented Jan. 25, 1966 being drawn into the presence of the leeward portion of the conduit.

Other objects and features of the invention will be appreciated and become apparent as the present disclosure proceeds and upon, consideration of the accompanying drawing and the following detailed description wherein an embodiment of the invention is disclosed.

In the drawing:

FIG. 1 is an elevational view of a vertically disposed conduit or stack showing the upper'en'd portion in section and with the protective device in association therewith.

FIG. 2 is a -sectional view taken on the line 2-=2 of FIG. 1.

FIG. 3 is a sectional view taken on the line -3-3 of FIG. l.

FIG. 4 is a fragmentary flat projection view of the protective device.

FIG. 5 is a plan view ot'the assembly on a smaller scale.

Referring to the drawing there is shown at 10 a vertically disposed conduit which may be employed for discharging waste gases through the open upper *end 11. The conduit 10 may be employed as a smoke stackor as a flare stack burner when the dump gases are ignited and combustion takes place adjacent the open upper end 11. Such a vertically disposed conduit is subjected to wind currents anda low pressure condition-is developed on the leeward side of the conduit 10 as a result of air moving transversely of the stack. A low pressure 'zone is developed by the air currents flowing about the conduit structure in flow patterns which creates a void at the downwind side of the stack. Any gases which are corrosive or the heat and. the products of combustion of a flare stack burner are "drawn downwardly into this low pressure zone and into the presence of the conduit so that they attack the conduit.

In carrying out the presentinvention a device -is mounted on the upper end portion of *the stack 10 which .prevents the development of a low pressure zone at the leeward side thereof. The protective device takes the form 'of a cup-shaped member 12 having a cylindrical wall 14 and an end wall 16. The cylindrical wall 14 is of larger diameter than the stack or conduit 10 to provide an annular chamber -or;space 15 between the exterior of the conduit 10 and the interior "of the wall 14. The end Wall 16 is of ring shape "and closes the lower end of the annular chamber *15. Theend Wall 16 may be welded or otherwise secured to the exterior '{of the. stack or conduit 10 and it may be formed integral with the cylindrical wall portion 14. The, end '{wall 16 provides support for the cylindrical portion 14 "and gusset webs '18 may be welded or otherwise secured to the conduit or'stack 10 and to the end wall lfi to ma'intain the cup-shaped member 12 in fixed relationship with the upperend of the stack.

The cylindrical wal1-portion 14 of the fcup-shaped member is .provided with a plurality 01. holes which arearranged in spaced relationship. The *holes are arranged in horizontal and vertical alignment as best shown in FIG. 4. One series of holes 21 are arrangedas a vertically aligned row. An adjacent series of holes -22 are arranged as a row and' in vertical alignment. The h'oles 21 are also arranged as a horizontal'row and the holes 22 are arranged in horizontal alignment with each other. The peripheral portion of one series of holes -21 -slightly overlaps the peripheral portion of the adjacent series of holes 22 as indicated by the line T in FIG. 4 which is tangent to the holes 21 and the purpose of such a disposition of the openings will be more apparent as the present disclosure proceeds.

It will be observed from a consideration of FIG. 5 that when a wind current is in the direction of the arrow 25 a pressure is developed in the zone X which is greater than atmospheric throughout an upwind sector of the cylindrical wall 14. A pressure less than atmospheric is created in the zone Z at the downwind side of the cylindrical wall 14. As a consequence air will move into the openings 21 and 22 in the direction of the arrows shown in FIG. 2. The air entering through the openings 21 and 22 at the upwind side of the cylindrical wall 14 moves in the directions of the arrows shown in FIG. 2 and some of the air escapes through the openings 21 and 22 at the leeward side of the cylindrical wall.

The openings at the upstream sector ofthe device 12 and at the downstream sector are of same size and shape. These openings may for example be designed to have a flow coefficient of 0.61. Accordingly of that quantity of air which enters the openings at the upstream sector of the cylindrical wall 14 only sixty-one percent can escape through the openings in the downstream side. That portion' of the air which does not escape through the openings at the downstream side of the cup-shaped member 12 moves upwardlyas shown by the arrows 26 in FIG. 1 and escapes through the open upper end 27. The upward movement of air in the direction of the arrows 26 at the downwind side of the assembly counters any tendency of the gaseous products at the upper end 11 of the stack to move downwardly over the leeward part of conduit 10.

The holes 21 and 22 are staggered and portions of their peripheries overlap as indicated by the tangent line T. This is for the purpose of preventing the development of substantiallyvertically extending low pressure zones outside the member 12 throughout the leeward sector thereof. If all ofthe holes were in vertically aligned rows with one row circumferentially spaced from another row there would be a narrow vertical zone of low pressure between'each row of holes outside the member 12 and the gaseous products escaping through the open end 11 would be drawn downwardly into these low pressure areas. The staggering of the holes 21 with reference to the holes 22 avoids the development of such low pressure zones and by slightly overlapping the peripheries of the holes as shown by the tangent line T the possibility of low pressure zones being developed within the downwind portion of the member 12 is completely avoided. The closure of the bottom of the annular space or chamber 15 prevents "any low pressure condition developed at the leeward side of the stack or conduit below the protective device 12 from influencing the conditions within the annular space and the flow patterns of the air therein. It has been found that the ratio of the area of all of the openings 21 and 22 to the total area of the cylindrical wall 14 should be between 0.2 and 0.5.

While the invention has been described with reference to particular structural shape for the protective device in association with one type of the vent conduit or stack it will be appreciated that the structure of the overall assembly may be varied and changes may be made in the respective elements. Such modifications and others may be made without departing from the spirit and scope i the lower portion of said wail providing closure of the lower end of said annular space, said cylindrical wall having unobstructed circular holes therethrough spaced from each other, said holes being arranged in substantially vertically aligned circumferentially spaced rows throughout said cylindrical wall, the holes of one row being staggered vertically with respect to the holes of an adjacent row, all of said holes having substantially the same flow coefiicient, and vertically extending tangents of the holes in one row forming vertical chords with respect to the holes of laterally adjacent rows of holes.

2. A protective device in combination with an upright stack consisting of, conduit means arranged in a generally vertical position and exposed to transverse air currents from any direction, said conduit means having an open upper end, an annular Wall embracing an upper end portion of said conduit means in space relationship providing a substantially uniform annular space between the exterior of the conduit means and the interior of said wall, impervious means joining the perimeter of said conduit means with the lower portion of said wall, said wall having spaced holes throughout all circumferential portions thereof, all of said holes having substantially the same flow coefiicient, vertical projections of the perimeter of lowermost of said holes overlapping portions of the holes thereabove whereby air enters said holes at the windward side of said wall and escapes through holes at the leeward side of the wall to relieve low pressure at the leeward side thereof with some of the air flowing upwardly in said annular space at the leeward side of the stack.

3. A vent stack and a protective device consisting of, a substantially cylindrical upright conduit exposed to transverse air currents from any direction, said conduit having an open upper end for escape of gas, a wall surrounding an upper end portion of said conduit in spaced relationship providing a substantially annular space between the exterior of the conduit and the interior of said Wall, the holes of one row being staggered with respect to the lower portion of said wall providing closure of the lower end of said annular space, said wall having unobstructed holes therethrough spaced from each. other, said holes being arranged in substantially vertically aligned circumferentially spaced rows throughout said wall, the holes of one row being staggered with respect to the holes of an adjacent row, all of said holes having substantially the same flow coefiicient, vertical extensions of tangents of the holes in one row forming vertical chords with respect to the holes of laterally adjacent rows of holes, and the area of all of said :holes being greater than 0.2 and less than 0.5 of the total area of said wall.

4. A vent stack and a protective device consisting of, an upright conduit exposed to transverse air currents from any generally horizontal direction, said conduit having an opening in the upper end of the escape of gaseous materials, a wall surrounding an upperend portion of said conduit in spaced relationship providing a generally annular space between the exterior of the conduit and the interior of said wall, means extending from said wall to said conduit closing the lower end of said space, said wall having unobstructed holes therethrough vertically and horizontally spaced from each other with all of said holes having substantiallythe same flow coefficient, and a vertically extending line defining the perimeter of, any one of the uppermost holes intersecting a hole therebelow. Y

No references cited.

FREDERICK L, MATTESON,.IR., Primary Examiner. 

1. A VENT STACK AND A PROTECTIVE DEVICE CONSISTING OF, A SUBSTANTIALLY CYLINDRICAL UPRIGHT CONDUIT EXPOSED TO TRANSVERSE AIR CURRENTS FROM ANY DIRECTION, SAID CONDUIT HAVING AN OPEN UPPER END FOR ESCAPE OF GAS TO ATMOSPHERE, A SUBSTANTIALLY CYLINDRICAL WALL SURROUNDING AN UPPER END PORTION OF SAID CONDUIT IN SPACED RELATIONSHIP PROVIDING A SUBSTANTIALLY ANNULAR UNOBSTRUCTED SPACE BETWEEN THE EXTERIOR OF THE CONDUIT AND INTERIOR OF SAID WALL, MEANS JOINING THE PERIMETER OF SAID CONDUIT WITH THE LOWER PORTION OF SAID WALL PROVIDING CLOSURE OF THE LOWER END OF SAID ANNULAR SPACE, THERETHROUGH SPACED HAVING UNOBSTRUCTED CIRCULAR HOLES THERETHROUGH SPACED FROM EACH OTHER, SAID HOLES BEING ARRANGED IN SUBSTANTIALLY VERTICALLY ALIGNED CIRCUMFERENTIALLY SPACED ROWS THROUGHOUT SAID CYLINDRICAL WALL, THE HOLES OF ONE ROW BEING STAGGERED VERTICALLY WITH RESPECT TO THE HOLES OF AN ADJACENT ROW, ALL OF SAID HOLES HAVING SUBSTANTIALLY THE SAME FLOW COEFFICIENT, AND VERTICALLY EXTENDING TANGENTS OF THE HOLES IN ONE ROW FORMING VERTICAL CHORDS WITH RESPECT TO THE HOLES OF LATERALLY ADJACENT ROWS OF HOLES. 